The present invention relates to a method and an apparatus for charged particle beam exposure that control charged particle beams and exposes a pattern of LSI and the like on a sample, more particularly to a method and an apparatus for charged particle beam exposure that use a plurality of charged particle beams.
In a charged particle beam exposure apparatus, such as an electron beam exposure apparatus, which exposes an LSI pattern on the sample by using the charged particle beams, a multibeam exposure system using a plurality of the charged particle beams has been proposed for improving the processing capability (throughput) of the apparatus. As an example of the conventional art of the multibeam exposure system, a blanking aperture array system is cited (H. Yasuda, J. VAC. Sci. Technol., B14 (6), 1996). In this system, a blanking aperture array formed of a plurality of aperture groups is used, which has a blanking electrode capable of independent control of an applied voltage. An electron beam from a single electron source is divided into a plurality of electron beams, and turning on/off of each electron beam is controlled by the blanking electrode capable of independent control. Thus, a beam shape formed by the group of the electron beams that consist of a plurality of the electron beams can be arbitrarily set. Accordingly, the throughput of the apparatus is improved because the electron beam of any shape can be obtained.
In the above-described conventional art, the dimension of the electron beam divided by the blanking aperture array is as large as approximately 100 nm on the sample, and the system is the one that divides the single charged particle beam. There existed a problem that the number of charged particle beams obtained has been limited to several hundred to one thousand, which has caused limitation to a dimension control of a pattern to be exposed and insufficient resolving power. In addition, error occurs in the exposure of proximate portions due to exposure dose distribution generated by scattering of the electrons in resist, reflected electrons from a sample surface or the like. There existed another problem that a special processing process has been required for a proximate effect correction for correcting the error. Such problems are apt to be more apparent as the exposure pattern becomes finer.
In the blanking aperture array system in the prior art lightens the problems as follows. Firstly, regarding the problem of insufficient dimension resolving power, a method for controlling an exposure dimension in a dimension unit finer than an electron beam dimension obtained by dividing the electron beam is disclosed in Japanese Patent Laid-Open No. Hei6(1994)-302506 gazette. This method is the one in which a pattern dimension is controlled in a finer dimension than the electron beam dimension, which is performed as follows. The apertures of the blanking aperture array are formed such that the apertures that belong to adjacent columns are arranged in the finer dimension unit than the dimension of the aperture in a shifted state. As apertures for exposing an end portion of the pattern, the apertures in a shifted relation are selected from each column in plural numbers in accordance with the dimension of the pattern to be exposed. Then, each of the electron beams generated from the apertures is irradiated in a superposing manner to control exposure dose at the end portion of the pattern. In this system, a high processing accuracy is required for processing the apertures in a positional accuracy between the apertures. Moreover, a higher processing accuracy and an increase of the number of apertures are required in order to make a dimension control resolving power finer by improving the resolving power of a shift amount. Furthermore, there exists a problem that a control circuit of the blanking aperture array becomes complex because selection of the apertures for exposing the end portion of the pattern is necessary depending on the pattern dimension.
The proximity effect correction is the one, as disclosed in Japanese Patent Laid-Open No. Hei5(1993)-175018 gazette, No. Hei5(1993)-206016 gazette and No. Hei6(1994)-53129 gazette, in which a correction exposure process is performed for correcting an exposure dose error by a proximity effect occurred in an exposure process in addition to an actual pattern exposure process. In this method, reduction of the throughput is inevitable because the number of exposure processes is increased. As a method that does not require the correction exposure process, there exists a system as disclosed in Japanese Patent Laid-Open No. Hei9(1997)-63926 that data in which exposure data for correcting the exposure error by pattern data is added to the pattern data is formed prior to exposure and a corrected pattern is obtained by one exposure process. In this system, a long time is consumed since conditions need to be obtained by generation of the pattern data and a test writing, which leads to reduction of a total throughput of the apparatus.
In the present invention, a charged particle beam exposure method and a charged particle beam exposure apparatus described in each claim are adopted to solve the problems in the above-described conventional art. A beam source may be either plural or single. Specifically, in the charged particle beam exposure apparatus that exposes an LSI pattern or the like by irradiating a group of the charged particle beams formed by a plurality of the charged particle beams on a sample, the charged particle beams that constitute a plurality of the charged particle beam groups is irradiated in a superposing manner to a specified section of a specified pattern (a charged particle beam section) to obtain a predetermined exposure intensity. Thus, a desired charge quantity is irradiated on a desired point on the sample, and a desired exposure dimension is obtained.
In addition, a plurality of the charged particle beams are used, of which current quantities are made to have a weighted gradation, the desired charge quantity is irradiated, and thus the desired exposure dimension is obtained.
A map for a number of shots determined by the dimension resolving power in a mesh and an exposure dose map based on introduction of an existence density concept of the pattern across a plurality of meshes are formed, and data of the maps is given to the charged particle beams side as data. Accordingly, the charged particle beams are allowed to have a high gradation capable of the exposure dose correction necessary for the proximate effect correction.
Therefore, even if the size of the mesh allocated on the sample is large, the number of gradations can be set by finely controlling an irradiated charge quantity of the charged particle beams and high dimension controllability is obtained. Thus, the number of beams forming the charged particle beam group can be considerably reduced and the beam source and a control apparatus can be simplified. Additionally, since the data for irradiation is corrected regarding the proximate effect correction, the throughput is improved because a special process is not required.